Review and Measurements of Fiio K5 Headphone Amp

[JohnYang1997]

Hope it helps, but Russ White got an 10mH inductor in parallel with a 22Ohms resistor: http://www.twistedpearaudio.com/docs/linestages/ventus_ez_schematic.pdf, others found a different way to reduce output impedance without affecting the stability.

PA probably did something similar, otherwise couldn't achieve 3mOhms of output impedance: http://sjostromaudio.com/pages/index.php/hifi-projects/128-qrv07-headphone-amp?start=6.

L.E.: Actually I don't know how PA achieved that low output imepdance, maybe he simply connected the TPA6120A directly to the headphones jack after all: http://sjostromaudio.com/pages/index.php/hifi-projects/128-qrv07-headphone-amp?showall=1 and http://sjostromaudio.com/hifi_pics/hifi_100pr/qrv07r0_TPA6120.jpg might help, but I see that the two 10.2Ohms blue resistors are connected directly to the output pins and I guess from J1/J2 jumpers these resistors could be shorted. Also, on QRV09 the output impedance is 10/120Ohms: http://sjostromaudio.com/pages/index.php/hifi-projects/130-qrv09-headphone-amp?start=5

There are many ways to make tpa6120 stable at low overall output impedance.
1, your first way.
2, zobel networks.
3, composite amplifier.
I'm not sure how fiio did it. But i have a tpa6120 amp has 0.0001% distortion from 20hz-2khz(rises afterwards) using composite amplifier topology. And it's very stable.

 

[JohnYang1997]

It seems that they have 10ohm resistor at the output (looks like 100 on the smd resistor)
It's very likely that they wrap opa1642 around the tpa6120a2 to achieve low output impedance with global feedback.

 

[JohnYang1997]

Besides that it seems that geekout v2 has low output impedance too.

 

[tired_guru]

I can tell that the atom now has become a new benchmark for Amir when comparing other amps. Nice, really nice

I can tell you own one beacuse it's been a while since we had atom's review here.

 

[Jimmy]

The two resistors are 1R0=1ohm (1.0), if you click over the pictures on the link that was posted you'll get high res pictures where the part markings are readable.

View attachment 22198View attachment 22199View attachment 22200
It seems that they have 10ohm resistor at the output (looks like 100 on the smd resistor)
It's very likely that they wrap opa1642 around the tpa6120a2 to achieve low output impedance with global feedback.

 

[JohnYang1997]

The two resistors are 1R0=1ohm (1.0), if you click over the pictures on the link that was posted you'll get high res pictures where the part markings are readable.

Sorry but on the site I saw I couldn't get a clearer picture.
So it's 1ohm output resistor then. Probably they used higher Rf to make it slower to stabilize tpa6120. But that doesn't work very well for capacitive load.
And I just realized that opa1642 is so far away and there are coupling capacitors so it couldn't be composite amplifier.

 

[WondrousHippo]

I had this thing for a while before selling it because it just didn't fit in my setup anymore. Thought this amp sounded good, glad Amir's measurements show that to be the case. I liked the volume knob, very easy to manipulate with just a finger!

Interestingly, Fiio removed the micro USB on the back in a future revision because they couldn't get the 11-pin micro-USB working in cable form, IIRC.

 

[pantag]

Looking forward to the Fiio K3 review! It would be great to see what kind of good DAC/Amp portable combo (USB bus-powered) you can get for around $100+ . Curious to see if it can drive the 300 Ohm Senn HD650, as Fiio claims only up to 150 Ohm headphones. Currently have the Fulla 2 but it is not very clear nor powerful.

 

[graz_lag]

Looking forward to the Fiio K3 review! It would be great to see what kind of good DAC/Amp portable combo (USB bus-powered) you can get for around $100+ . Curious to see if it can drive the 300 Ohm Senn HD650, as Fiio claims only up to 150 Ohm headphones. Currently have the Fulla 2 but it is not very clear nor powerful.

Does the Fulla-2 work with Android / OTG cable ?
My old Fulla-1 did not ...

 

[pantag]

Does the Fulla-2 work with Android / OTG cable ?
My old Fulla-1 did not ...

Not sure, as I do not have an Android phone or tablet. It is pretty flexible however. Did you check the FAQ section at Schiit? I believe I did see something for Android for it (positive).

 

[Jimmy]

I've seen TPA6120 based designs where they just omitted the output resistors, I just don't know if that's really safe, certainly it's not what TI recommends.

Anyway FIIO is a reputable company so I guess they know what they are doing, maybe there's some trick they've used to achieve it, but it's hard to know just with the PCB pictures.

Sorry but on the site I saw I couldn't get a clearer picture.
So it's 1ohm output resistor then. Probably they used higher Rf to make it slower to stabilize tpa6120. But that doesn't work very well for capacitive load.
And I just realized that opa1642 is so far away and there are coupling capacitors so it couldn't be composite amplifier.

 

[Tonycanuck]

Thanks for this. Interesting timing as I own the K5 and I see that the Atom beats it, but is it so much superior that I would be better off selling the K5 and buying the Atom? Would I really care? I currently own both the 400i and 650, planning on saving up for something above $1k.

I do own a Fiio device, but I'm planning on getting a dedicated desktop DAC to play directly from my computer, so the dock won't matter either way.

Any thoughts, benefit to selling the K5 for the Atom? (Or El Amp if that matters)

Thanks!

 

[amirm]

Thanks for this. Interesting timing as I own the K5 and I see that the Atom beats it, but is it so much superior that I would be better off selling the K5 and buying the Atom? Would I really care? I currently own both the 400i and 650, planning on saving up for something above $1k.

How far do you go on the volume control? If it is not past 2:00 o'clock then you don't need the atom.

 

[Jimster480]

Very cool, this is actually a respectable offering even if it is beaten by the Atom.
Good to see that FiiO Delivers a competitive product once again. We need more companies like FiiO

 

[Tonycanuck]

How far do you go on the volume control? If it is not past 2:00 o'clock then you don't need the atom.

Nope, I'm below 2:00. That's great, thanks!

I'm assuming the El Amp by JDS would be similar?

(I was thinking of the El Stack for aesthetic reasons, although I might just get the El DAC and pair it with the K5, but just doesn't look the same...)

Keep up the great site, I'm learning a lot on here!

 

[Jimster480]

Nope, I'm below 2:00. That's great, thanks!

I'm assuming the El Amp by JDS would be similar?

(I was thinking of the El Stack for aesthetic reasons, although I might just get the El DAC and pair it with the K5, but just doesn't look the same...)

Keep up the great site, I'm learning a lot on here!

Yes I mean the performance of this amp is already good enough so you don't need to change it at all

 

[JohnYang1997]

Nope, I'm below 2:00. That's great, thanks!

I'm assuming the El Amp by JDS would be similar?

(I was thinking of the El Stack for aesthetic reasons, although I might just get the El DAC and pair it with the K5, but just doesn't look the same...)

Keep up the great site, I'm learning a lot on here!

El amp is essentially atom. The circuits are the same except the followings:
1, different opamps, lme49720 vs njm2068
2, ac coupled vs dc coupled
3, power supply use different chips.
The output network is completely the same with same value of resistors and capacitors, the feedback network is the same too.

 

[JohnYang1997]

In fact, the measurements from amir of element, the thd+n isn't very good because of the low frequency power noise residue. I have mine, when i measure it I don't see the power supply noise. Since the capacitors are the same values, i don't really see why there is difference. Sure probably lm317 is better and pcb layout is better. But distortion harmonics are actually lower on el amp.

 

[Guermantes]

Thanks for this review, Amir. I considered buying one of these to match my Fiio X3 DAP, so nice to see it measures respectably. However, I ideally want something to drive my Beyerdynamic DT880 600Ω headphones happily. If only the Atom wasn't so pricey here in the Antipodes . . .

 

[JohnYang1997]

Thanks for this review, Amir. I considered buying one of these to match my Fiio X3 DAP, so nice to see it measures respectably. However, I ideally want something to drive my Beyerdynamic DT880 600Ω headphones happily. If only the Atom wasn't so pricey here in the Antipodes . . .

High impedance headphones are not going to cause distortion nor sensitive to noise. If they are loud enough, they will sound good.
If you really want something to power them right, atom isn't going to be better than a simple opa1622 board or even a general use opa1612/opa827 opamp. Only high voltage swing discrete amplifier will be better than simple opamps. But there aren't cheap ones that have high voltage swing.
Btw if you are able to build your own amp. I recommend using lme49860 and running at +-22v using the circuit of o2 or 47amp. That's the cheap and effective solution for high impedance headphones.